Competitive exclusion of Salmonella colonization in chickens using a defined community of bacteria

Authors: WICKWARE, CARMEN - Oak Ridge Institute For Science And Education (ORISE); HARRIS, DYLAN - Oak Ridge Institute For Science And Education (ORISE); ATKINSON, BRIONY - Iowa State University; Bearson, Shawn; Monson, Melissa; Oladeinde, Adelumola - Ade; Anderson, Christopher; Looft, Torey

Submitted to: Conference Research Workers Disease Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 12/6/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: OBJECTIVE: Non-antimicrobial intervention strategies to decrease Salmonella load in pre-harvest poultry production are important to improve food safety and protect public health. Previous use of cecal contents from mature chickens has shown protection against Salmonella through competitive exclusion, an antagonistic relationship between two or more species. However, the composition of cecal contents is undefined and direct introduction to chicks could lead to variable results and safety concerns. The objective of this study was to determine if Salmonella colonization of chickens could be reduced through competitive exclusion using a defined community of chicken commensal bacteria. METHODS: One-day old White Leghorn chicks, hatched on-site, were randomly divided into experimental groups and given an oral gavage of either a defined community of 15 bacterial species (DC), cecal contents (CC), or sterile PBS (control; CT). After one week, birds were euthanized for cecal content collection (pre-Salmonella sample) while the remaining birds were orally gavaged 1 X 108 colony forming units (CFU) of Salmonella enterica ser. Heidelberg strain 2813 (SH2813). Bacterial counts for three post-Salmonella timepoints (3, 14, and 28 days post inoculation; dpi) were evaluated. Bacteriological enumeration was performed by plating cecal contents onto Salmonella selective agar to determine CFU/g in each group for all collection days. Cecal contents were also used for bacterial community analysis. Briefly, DNA was extracted from cecal contents and the V4 region of the 16S rRNA gene was amplified and sequenced. Sequences were used to examine the bacterial diversity as well as differences in abundance for each group. Significance was tested using Kruskal-Wallis for bacterial counts and alpha diversity, and perMANOVA for beta diversity. Multiple-test corrected p-values (adj.p) were used for all statistical tests. RESULTS: A 2 log10 reduction in SH2813 was observed in DC compared to CT at 28 dpi (adj.p < 0.05). SH2813 counts from the CC group were below 10 CFU/g for all timepoints. The bacterial community of CC showed significant differences in alpha and beta diversity compared to other groups for all timepoints (adj.p < 0.05). The bacterial community in DC birds had lower diversity and abundance compared to CT birds on day 14 but diversity in DC was closer to CT on 28 dpi. In examining the relative abundances of the top genus-level operational taxonomic units (OTU; 97% sequence similarity) shared across the three groups, CC had high relative abundances of several OTUs for all sample times (> 10% each OTU). In comparison, during the first two sample points DC samples had high relative abundances of OTUs belonging to the same genera as members contained within the initial treatment gavage, though there were fewer overall OTUs. CONCLUSIONS: Though birds receiving cecal contents had improved protection against SH2813 colonization, DC showed a reduction in SH2813 when compared to the control. The reduction shows the potential of defined microbial communities to reduce Salmonella colonization. Moving forward, studies to establish the optimal community should include load of DC given, timing of Salmonella exposure, and potential cross-protection.